The goal of this R21 PROJECT is two-fold: 1) to increase our understanding regarding the effects of spinal manipulation on the nervous system and 2) to seek a scientific basis for the continued investigation of the role of proprioceptors in the effects of spinal manipulation. The specific aim of this project is to determine if the speed of a spinal manipulation is an important determinant of the neural response from paraspinal muscle proprioceptors. Strong evidence supports using spinal manipulation to help patients with acute low back pain and neck pain. A theory common to the practice of spinal manipulation proposes that spinal manipulation alters paraspinal sensory input (ie, neural input from tissues of the vertebral column). Preliminary data demonstrate that spinal manipulative impulses stimulate proprioceptive afferents from lumbar paraspinal muscles. These afferents could contribute to the therapeutic effects of manipulation. The proposed experiments will determine how muscle spindles and Golgi tendon organs in lumbar paraspinal muscle respond to the time-varying impulse of a spinal manipulation. Slow and fast impulses will be given. A Fourier transform will be used to analyze, in the time domain, the force-time and displacement-time profile of each manipulative impulse. The resulting power spectra for a range of impulse durations will enable us to determine if the speed of a spinal manipulation is an important determinant of proprioceptive sensory input from paraspinal muscles during spinal manipulation. The experiments will provide information regarding the neural systems impacted by spinal manipulation and can lead to improved training methods for the proper application of spinal manipulation . Teaching the manual skill of spinal manipulation could be approached from the perspective of quantifying the velocity with which the clinician applies a spinal manipulation.